1. Field of the Invention
The invention relates to a stainless steel and a method of manufacturing the same. In particular, the invention relates to a stainless steel suitable for exhaust system component that require anticorrosion against both of general corrosion and local corrosion, and a method of manufacturing the same.
2. Description of Related Art
In the stainless steel, anticorrosion against both of general corrosion and local corrosion is required. However, when the stainless steel is used for exhaust system parts of an internal combustion engine, it is required to prevent pitting corrosion from occurring even during the use of inferior fuel.
As such a stainless steel and a method of manufacturing the same, for example, there is a method in which a concentration ratio of chromium (Cr) and iron (Fe) is controlled in a superficial layer by mechanical polishing for forming surface unevenness and a chemical treatment for strengthening a passive film, and the ratio of chromium (Cr) concentration and iron (Fe) concentration in the superficial layer is increased more than that in a matrix phase (see, for example, Japanese Patent Application Publication No. 2012-170961 (JP 2012-170961 A)).
Further, a stainless steel in which a chromium concentration within 10 nm of a superficial layer is reduced and the acid pickling property is increased thereby (see Japanese Patent Application Publication No. 2001-234300 (JP 2001-234300 A), for example), a stainless steel that is surface modified by volatilizing manganese (Mn) that has a high vapor pressure among main constituent elements (see Japanese Patent Application Publication No. 04-131321 (JP 04-131321 A), for example), and a stainless steel in which a chromium content is set in the range of 0.25 to 11.5 wt % by weight and general corrosion resistance and local corrosion resistance are improved thereby (see Japanese Patent Application Publication No. 02-54740 (JP 02-54740 A), for example) are known.